1. Field of the Invention
This invention relates to a socket for mounting electrical components on a printed circuit board and more particularly relates to a multicontact surface mount socket for mounting an integrated circuit package on a printed circuit board.
2. Description of the Prior Art
Socket assemblies adapted to receive electronic components or packages and which can be connected by leads through apertures in printed circuit boards to printed circuits by means of DIP soldering or wave soldering techniques are in wide use, especially for mounting components such as dual in-line packages which comprise components having leads extending from an encapsulated integrated chip package. For example a conventional dual in-line package comprises a plastic housing, in which an integrated circuit is insert molded and has a plurality of leads extending in parallel rows to opposite sides of the plastic package. Typical dual in-line packages might have 14 leads although other sizes are available.
Although dual in-line packages can be attached directly to printed circuit boards, having plated-through holes for receiving the leads, a common practice is to use a separate socket for establishing a mechanical connection to the leads of the dual in-line package. The separate socket has in turn a spring loaded portion for engaging the dual in-line package lead and an extending lead for receipt in a plated-through hole in a circuit board. One example of a dual in-line socket having a leaf spring arrangement received and soldered in a hole in a printed circuit board is shown in U.S. Pat. No. 3,696,323, wherein the leads are soldered directly to traces on the lower surface of the printed circuit board. Sockets of the type disclosed therein are employed because the DIP leads can be damaged during insertion in the printed circuit board or during the soldering operation. A further disadvantage of soldering a DIP directly to a printed circuit board is that soldered DIP packages are difficult to replace. Another conventional socket for use with DIP packages is disclosed in U.S. Pat. No. 4,060,296.
Although through-hole interconnection of DIP packages and sockets represents the conventional manner of interconnecting integrated sockets to a printed circuit board, increasing use is being made of surface mount techniques to interconnect integrated circuitry to mounting pads located directly on the surface of a printed circuit board. Surface mount techniques generally employ a predeposited solder paste located on surface mount pads, to which a component such as a chip carrier or a simple electrical component such as a resistor are attached. The component is first positioned in registry with the surface mounting pad and then the component is soldered directly to the surface mounting pad. Surface mount soldering operations include vapor phase reflow soldering and infrared heating, both widely accepted methods of surface mount soldering.
By attaching individual components and component receptacles directly to the surface of a printed circuit board, the amount of board real estate required to mount individual components is reduced, thus allowing greater density of the components on the board. Although surface mounting of components on printed circuit boards offers many advantages, a great many common electrical components, such as dual in-line packages which are employed in numerous systems are not amenable to direct surface mounting. In part, the difficulty in directly mounting the leads of a dual in-line package directly to surface mount pads on a printed circuit board is attributable to the stresses induced as a result of differing coefficients of thermal expansion between the printed circuit board and the dual in-line package. The forces generated as a result of thermal cycling thus would place significant stress upon the leads. Since a surface mount solder connection is inherently weaker than a through-hole connection, in part because of the amount of solder and surface area available for solder, these stresses can cause significant difficulty with surface mounted components. Thus the use of a conventional dual in-line package with other surface mount components on a printed circuit board would require two separate soldering operations, such as a vapor phase reflow soldering operation for attachment of surface mount components to the printed circuit board and the conventional wave soldering operation to attach the leads from a DIP package or a conventional DIP socket to conductors on the lower surface of the printed circuit board. Thus a user would not be able to simultaneously realize the advantages of surface mount technology while still employing conventional dual in-line package electronic components in its circuitry. The instant invention provides a means for surface mounting a dual in-line package to a printed circuit board to permit the user to realize the advantages of surface mount components while still employing conventional dual in-line packages which have proved to be satisfactory components of its electrical system.